The Food and Drug Administration has asked Regeneron Pharmaceuticals Inc and Sanofi SA to assess potential neurocognitive side effects of their experimental cholesterol drug, Sanofi said in its annual report on Friday.
Amgen Inc, which is developing a similar drug, said it has also been in communication with the agency.
The FDA said it could not discuss specific development programs, but is "aware of concerns raised with neurocognitive adverse events and other lipid-lowering therapies, including statins, and as part of our oversight of new drug development, we are carefully monitoring these events."
The new drugs are part of an experimental class known as PCSK9 inhibitors designed to block a protein that maintains "bad" LDL cholesterol in the bloodstream.
"We have not seen a neurocognitive adverse signal in the alirocumab data," Dr. Michael Aberman, Regeneron's vice president for strategy and investor relations, said in a telephone interview.
He said the alirocumab trials have been overseen by independent safety monitors.
"What the FDA asked us to do we don't expect to be difficult or time consuming," Aberman added.
Sanofi and Regeneron said they did not know how the FDA learned of the potential side effects, and they were not aware of any such side effects with alirocumab.
Pfizer Inc, also in the late stages of developing a PCSK9 drug, said in an emailed statement that it has not received a similar request from the FDA but is already assessing potential neurocognitive side effects in late-stage trials of its drug, bococizumab. "At this stage of our bococizumab development program, we are not aware of any neurocognitive safety signals," the company said.
Amgen, which has said it could file for regulatory approval of PCSK9 drug evolocumab this year, said it has been proactively monitoring for cognitive impairment in its trials.
"Similar to other companies developing PCSK9 inhibitors, Amgen has been in communication with the FDA, and we will continue to investigate the potential for cognitive impairment in our program," Amgen said in an emailed statement.
The company said it has not seen any such signal so far.
Sanofi's report echoed a filing made by Regeneron last month, in which the company said the FDA advised it was aware of adverse neurocognitive effects associated with PCSK9 inhibitors.
Shares of Regeneron fell as much as 10 percent before paring losses to close down 3 percent, while shares of Amgen dropped 1.5 percent. U.S.-listed shares of France-based Sanofi fell 1 percent.
Rare side effects such as memory loss, impaired concentration, and paranoia have been associated with the use of statins for lowering LDL cholesterol, and their labels include warnings about cognitive impairment.
Statins, such as AstraZeneca PLC's Crestor and generic forms of Pfizer's Lipitor, are the most widely used cholesterol-lowering treatments and work by blocking the liver's production of LDL cholesterol.
"While we continue to believe the PCSK9 class has multi-billion dollar potential, we note that increased speculation on adverse events may increase the probability that the FDA could require outcomes data prior to full approval," JP Morgan analyst Geoff Meacham said in a research note.
The FDA said last year that PCSK9 drugs could get regulatory approval based on their ability to lower bad cholesterol, and may not need to show that they reduce the risk of heart attack and stroke.
In their filings, Sanofi and Regeneron said that if studies detect neurocognitive or other adverse side effects, development of alirocumab could fail or be delayed.
(Reporting by Deena Beasley; Additional reporting Bill Berkrot; Editing by Dan Grebler, Meredith Mazzilli and Marguerita Choy)